Purpose: The objective of this work was to evaluate the effectiveness of the combined thermal and chlorine dioxide gas (ClO2) treatment with mechanical mixing (tumbling) to eliminate Salmonella on artificially inoculated mungbean seeds.
Methods: Mungbean seeds were artificially inoculated with Salmonella Montevideo and stored at 4°C for 24 h. The effectiveness of inactivating Salmonella cells on the inoculated seeds using wet or dry heat with or without gaseous ClO2 (3.5 mg/l air) was investigated. The role of tumbling (mechanical mixing) during treatments on inactivating Salmonella cells was also investigated.
Results: Although no viable Salmonella was recovered from seeds treated in hot water at 60°C for 2 h, these treated seeds failed to germinate. Dry heat treatments (55, 60, or 70°C) for up to 8 h reduced Salmonella populations in excess of 3 log CFU/g. The use of tumbling while treating the seeds resulted in up to 1.6-log CFU/g reduction in Salmonella populations as compared to no tumbling. The combined treatment (70°C-ClO2-tumbling for 4 h) reduced Salmonella cells by 5 log CFU/g. All dry heat treated seeds were capable of germinating as well as the non-treated controls.
Significance: The data presented here suggested that thermal and ClO2 gas treatments were capable of penetrating and inactivating cells which are attached to inaccessible sites and/or are within biofilms on the seed surface. The increased reductions in pathogenic populations on the seeds with the use of tumbling could be attributed to increased uniformity of heat transfer and exposure to chlorine dioxide gas. The results presented here suggest that the combined treatment with tumbling would be a viable process for enhancing the safety of fresh sprouts.